A team of researchers, including a Georgia Institute of Technology
adjunct professor, has fired a new volley in the continuing
scientific debate over claims that a meteorite found in Antarctica
contains evidence of life on Mars.

In a paper to be published in the July issue of the journal
Meteoritics and Planetary Science, the researchers report evidence
that crystals found in the meteorite were formed by epitaxial
processes at temperatures that were likely too high for biological
organisms to exist. The findings cast new doubt on claims by NASA's
Johnson Space Center (JSC) researchers (led by David S. McKay) that
the so-called "Mars rock" contains forms consistent with nanofossils.

Using transmission electron microscopy, researchers discovered that
magnetite crystals in the meteorite, known as ALH84001, were
atomically intergrown with the surrounding carbonates by a rigorous
form of epitaxy. This process is an ordered growth of one mineral
on top of another. The resulting complementary orientation of
crystals means the magnetites and carbonates must have grown
simultaneously at temperatures much greater than 120 degrees
Celsius, researchers said.

Epitaxial formation rules out intracellular precipitation of the
magnetites by Martian organisms, a theory hypothesized by NASA
scientists who believe the meteorite contains nanofossils, the Tech
researchers said. And the implied high-temperature origin virtually
eliminates the possibility that fossilized Martian organisms exist
in this meteorite, they added.

This article is the third in a series of this research team's
technical papers that have disputed claims of biological life in
the meteorite. The other papers were published in the journals
Geochimica et Cosmochimica Acta (1996) and Nature (1997). NASA has
sponsored all of this research, as well as work by JSC scientists
who made the nanofossil claims.

"These three papers in combination basically invalidate much of
their (JSC's) evidence," said Dr. John Bradley, an adjunct
professor in the Georgia Tech School of Materials Science and
Engineering and executive director of MVA Inc., a microanalytic
company in Norcross, Ga. "Early skepticism has evolved into
international consensus among meteoriticists and planetary
scientists, with the exception of the JSC team, that this rock does
not contain Martian nanofossils. I do not know of a single other
individual who believes it at this point."

Bradley conducted the current and previous research with Drs. Hap
McSween of the University of Tennessee in Knoxville and Ralph
Harvey of Case Western Reserve University in Cleveland, Ohio. In
their first paper, the researchers used transmission electron
microscopy (TEM) to discover that elongated forms in the meteorite
contained crystallographic defects that look like a spiral
staircase, Bradley said. These defects, called screw dislocations,
typically form during high temperature vapor phase growth.

The JSC team, using field emission scanning electron microscopy, had
claimed that these worm-like, elongated forms were nanofossils. If
true, they should contain internal "daisy chains" of aligned
magnetite crystals called magnetosomes. Bradley's team found
elongated, rod-shaped magnetites called "whiskers" instead. But JSC
researchers countered that the differences resulted from scientists
using different microscopy techniques and thus seeing different
objects.

So Bradley's team duplicated the JSC researchers' scanning electron
microscopy (SEM) procedures at Georgia Tech using the same metal
coatings, gold and palladium, to make the specimen surfaces
conductive. With SEM, Bradley's team found the same worm-like
objects. Then, however, they rotated and tilted the meteorite
specimens to get a different microscopic angle. From that
perspective, the worm-like objects appeared to be inorganic mineral
lamellae or protruding ledges. Their worm-like segmented surface
structures were actually artifacts of the gold and palladium
coatings on the specimens. "They looked like the edge of a stack of
copy paper in which a few pages are sticking up on edge," Bradley
said.

In a rebuttal paper accompanying the Bradley team's 1997 article in
Nature, the NASA researchers conceded that these non-biological
worm-like structures are present in the meteorite, but that their
nanofossils are "different."

"It's like looking for worms in a plate of spaghetti," Bradley
said. "If the worms look like spaghetti noodles and they're not
wriggling around, how can you be sure they're worms and not
noodles?"

In the current paper, researchers focus on epitaxially grown
magnetite single crystals. They are key indicators of the
geochemical and thermal history of the carbonate-rich fracture
zones of the Martian rock, they said. Magnetite crystals,
apparently formed by several high temperature growth mechanisms,
are found in several distinct mineral settings in this meteorite.

With regard to whiskers, the researchers cite various evidence of
epitaxial crystal growth and high temperature origin of magnetites
in the meteorite. TEM techniques allowed researchers to view the
well-defined spatial orientation relationship between magnetite and
carbonate crystals. Epitaxy can occur if two similarly patterned
lattice planes of crystal structures are parallel. Previous studies
have shown the ideal lattice "misfit" between two crystal
structures should not exceed 15 percent. In this case, the lattice
"misfit" was only 11-13 percent, which is ideal for epitaxial
growth, Bradley said.

Furthermore, many of the epitaxially formed magnetite whiskers in
the meteorite appear to be free of internal defects, the
researchers said. Such is typically the case of crystals formed at
elevated temperatures, while those grown at lower temperatures tend
to have high densities of internal defects.

Also, researchers found epitaxially formed magnetite crystals in
mineral specimens from volcanoes in Indonesia and Alaska. These
crystals formed at temperatures in excess of 600 degrees Celsius,
researchers said. They compared these to the magnetites in the
meteorite because volcanoes also exist on Mars. The comparison
provided further evidence of a high temperature origin, Bradley
said.

Despite this paper and the other two Bradley team publications, the
debate over nanofossils in Martian meteorite ALH84001 will
continue, Bradley said.

"Unless the JSC team concedes, the debate will never die," Bradley
said. "When this news first became public, the debate was quickly
deflected into one about whether life exists or once existed on
Mars. But there are really two debates here -- whether there is
evidence of life in this meteorite and whether life exists on
Mars."

The first question is already answered in Bradley's estimation. The
second remains, and Bradley believes it is very unlikely that life
exists on the surface of Mars. "It may be down in the depths. We
now know that life thrives in very extreme conditions on Earth," he
said.

PHOTO CAPTION:
Dr. John Bradley presents electron microscope images of Martian
meteorite crystals that contain"nanofossils," according to some
scientists.

PHOTO COPYRIGHT INFORMATION: Photographs are copyrighted by the
Georgia Tech Research Corporation and may be freely used by the
news media with credit to the Georgia Institute of Technology. The
photographer is Stanley Leary, Georgia Tech Communications
Division.

University of California-San Diego

June 5, 1998

LIFE'S "SIGNATURE" NOT FOUND IN MARTIAN METEORITE ACCORDING TO NEW RESEARCH BY CHEMISTS AT UCSD

Grains of carbonate minerals believed to signal previous life on a Martian
meteorite are most likely non-biologic in origin, according to new studies
by chemists at the University of California, San Diego.

In a study reported in the current issue of the journal Science, the UCSD
scientists report that the carbonates laced through the potato-sized rock
are the product of reactions with atmospheric carbon dioxide.

"This data suggests that the carbonates were made by the interaction with
the atmosphere rather than with the water on the surface, as would be
required for a biologic process," said Mark Thiemens, professor of chemistry
and biochemistry at UCSD and principal investigator of the study. Other co-
authors of the study were UCSD chemists James Farquhar and Teresa Jackson.

The new results are based on the first multi-oxygen isotopic examination of
carbonate globules in the meteorite, named Allan Hills 84001 (ALH84001).
Isotopes are atomic elements that have the same chemical properties, but
different weights and slightly different physical properties.

In August 1996, research teams at NASA's Johnson Space Center and Stanford
University announced their belief that at least parts of the brown-colored
carbonates found in ALH84001 bore a striking resemblance to the earliest
microfossils on earth, suggesting past life on Mars.

To see if the origin of the carbonates could be determined, the UCSD
chemists measured the proportions of oxygen 16, oxygen 17 and oxygen 18
found in the sample, seeking clues in the form of clear isotopic
"signatures." An isotopic signature to achemist is what a fingerprint is to
a detective. For the carbonates, the UCSD scientists wanted to find out if
the fingerprints matched oxygen from the atmosphere or oxygen from the
hydrosphere.

If the signature pointed toward a water origin, that would support that
case for life, since on this planet and elsewhere, the genesis for all life
is water. If the signature matched the oxygen isotopes from the Martian
atmosphere, that would suggest a non-biologic origin.

"So if these things were biogenic, they should have equilibrated with
water," said Thiemens. "They didn't. They equilibrated with the atmosphere.

"What it looks like is that the Martian oxygen isotopes came from the
Martian carbon dioxide atmosphere. So what we're seeing looks like a garden
variety precipitate of carbonates, rather than life."

To continue his search for life's signature, Thiemens and other scientists
look forward to the next mission to Mars in 2005 when samples of the
atmosphere and rock are expected to be retrieved and returned to earth.

"In the meantime, there's a suite of Martian meteorites that we'll look
through and we'll do the same analyses," Thiemens said.

Funding for the UCSD study was provided by NASA.

Arizona State University

May 8, 1998

Study of sulfides in bacteria casts doubt on evidence of life in Martian
meteorite ALH84001

The Martian meteorite ALH84001 gave people hope that it was evidence for
extraterrestrial life because minerals found in it resembled minerals
created by some unusual earthly bacteria. Now it appears that the bacteria
themselves contradict that claim.

In an article appearing in the May 8, 1998 issue of Science, a team led by
two scientists from Arizona State University reports finding evidence for
as many as three different iron sulfide minerals in two different bacteria
known for generating magnetic compounds but not other iron sulfides normally
found with them.

One of the iron sulfides they did not detect is pyrrhotite, a mineral that
has been found in the now-famous Martian meteorite ALH84001 and that
frequently occurs as a breakdown product of the other sulfides. Though
pyrrhotite's presence in the meteorite has been cited as possible evidence
of past Martian bacterial life, the study's evidence suggests that the
bacteria may actually prevent its formation.

The study found evidence that the bacteria first produce mackinawite, a
nonmagnetic iron sulfide, which then naturally converts to the magnetic
greigite. It also suggests that this process may actually begin with cubic
iron sulfide, which is unstable and rapidly becomes mackinawite. In the
geological environment the bacteria are found in, the reaction sequence
would also eventually lead to greigite breaking down into pyrite and
pyrrhotite, but that reaction does not occur when the bacteria are present.

The team's research finding contradicts an earlier study that found pyrite
and pyrrhotite present in the bacteria. As no subsequent study has been able
to duplicate this result, the current team posits that earlier researchers
may have confused cubic iron sulfide with these minerals, which give similar
selected area electron diffraction patterns.

Latest research casts new doubt on evidence for fossil life in Martian
meteorite

New analyses of the famous Martian meteorite, ALH84001, have cast
additional doubt on the likelihood that it contains the fossilized remains
of ancient Martian microbes.

Two studies published last week find that much of the organic material in
the meteorite appears to be terrestrial, rather than extraterrestrial, in
origin. Richard Zare, the Marguerite Blake Wilbur Professor of Chemistry
at Stanford who headed the team that discovered organic material of
possible Martian origin in the potato-sized rock, says that the new findings
do not directly refute the original research. One of the analyses, however,
does suggest that the meteorite contains considerably more terrestrial
contamination than he had thought, Zare acknowledges.

ALH84001 was thrust into the limelight in August 1996 when a team of
scientists published a controversial analysis in the journal Science. They
argued that they had discovered organic material, unusual mineralogical
features and electron microscope images showing tiny oval and worm-
shaped features that, when taken together, provided compelling
circumstantial evidence that the meteorite was inhabited by Martian
microorganisms more than three billion years ago.

Scientists at NASA's Johnson Space Center in Houston provided the
electron microscope images of the putative nanofossils. Researchers from
the University of Georgia and McGill University contributed the
mineralogical evidence. Zare's research group produced data showing
that the meteorite contained a family of organic compounds called
polycyclic aromatic hydrocarbons (PAHs) that could have been produced
by the decomposition of alien microorganisms.

In the 17 months since the research was announced, other scientists have
published dozens of independent analyses that have both supported and
attacked the Martian microbe hypothesis. In the last month, however, the
weight of new research appears to be stacking up against the pro-life
position.

In December, John Bradley of MVA Inc. and Ralph Harvey of Case
Western Reserve University published a paper in the journal Nature that
attacked the NASA group's interpretation that the oval and worm-like
shapes that it reported could be the fossils of microorganisms. Duplicating
the NASA researchers' methods, Bradley and Harvey reported that all the
shapes that they could find in the meteorite are non-biological in nature
and consist of the fractured surfaces of common crystals. In the same
issue of the journal, the NASA team strongly contested this interpretation.

The two analyses of the organic material in the meteorite appeared in the
Jan. 16 issue of the journal Science.

A team from Scripps Institution of Oceanography, headed by Jeffrey Bada,
analyzed the meteorite for amino acids, the building blocks of life. They
found amino acids present in very low concentrations (between 7 parts
per million and 100 parts per billion). "What we found was that, yes, there
are amino acids in the meteorite at very low levels, but they are clearly
terrestrial and they look similar to amino acids we see in the surrounding
Antarctic ice," Bada said in a Scripps news release. (The meteorite spent
an estimated 13,000 years in the Antarctic ice before it was discovered.)

Bada based his conclusion that the amino acids were due to terrestrial
contamination on the results of an analytic technique called liquid
chromatography. The method determines the "handedness" of the amino
acids. Terrestrial organisms produce only left-handed amino acids, where
non-biological processes produce a mixture of left- and right-handed
molecules. Bada found that the amino acids in the meteorite were left-
handed and so concludes that they must be terrestrial. There is at least a
50 percent chance, however, that Martian life (if it exists) would also favor
left-handed molecules. So the experiment is by no means conclusive,
Zare said.

Even if the amino acids in the meteorite come from terrestrial
contamination, Zare says this does not prove that the PAHs which his
group found are also terrestrial in origin. "Amino acids are soluble in
water. So water provides a mechanism for carrying them into the interior
of the meteorite. But PAHs are highly insoluble and I don't know of any
mechanism that would transport them into the rock's interior where we
found them," he said.

Zare finds the second analysis, performed by a University of Arizona
research team headed by A. J. Timothy Jull, much more interesting and
compelling. "It is state-of-the-art and an extremely valuable study of the
degree of contamination in the meteorite," he said.

Jull's group burned samples of the meteorite at two different temperatures
to separate the organic carbon from the carbon contained in inorganic
minerals, which burn off at higher temperatures. They then analyzed the
isotopic ratios of the carbon from the two sources.

In previous work, Jull had determined that the carbonates in ALH84001
are substantially enriched in the isotope carbon-13 compared to those on
Earth. He and his colleagues interpret this as an indication that the carbon
dioxide in the early Martian atmosphere was also enriched in carbon-13.
If that is the case, then the tissue of Martian organisms would also have
elevated levels of carbon-13. When the team analyzed the ratio of carbon
isotopes in the organic carbon, however, it found that fully four-fifths of the
material had the same isotopic signature as terrestrial carbon. The other
20 percent appears to have a preterrestrial origin, they found.

"It looks like regular terrestrial organic material, with the exception of one
small component in ALH84001," Jull said in a University of Arizona news
release.

The analysis "indicates a much greater degree of terrestrial contamination
in the meteorite than I suspected was present two years ago," Zare said.
"In that sense, Jull's study does cast new doubt on our hypothesis that the
meteorite contains evidence of past Martian life."

On the other hand, the Stanford chemist does not believe that the study
completely rules out an extraterrestrial origin for the PAHs. "Jull's work is
for the whole rock. As in real estate, location is everything. His study does
not give any indication of the locations from which these different carbon
isotope fractions are coming. So I cannot tell where the PAHs, which are
concentrated around carbonate spheroids in the meteorite's interior, fall
in the terrestrial or preterrestrial fraction."

The saga of the provocative rock is far from over. Last summer NASA and
the National Science Foundation awarded grants for 23 new
investigations of AHL84001 as part of a coordinated program designed to
determine whether it contains traces of alien life. These studies will be
producing results in the next two to three years.

Although it may be decades before the significance of the meteorite is
determined conclusively, Zare sees several beneficial effects that are
independent of the debate's ultimate outcome. These include a
revitalization of research on meteorites, increased efforts to extend the
boundaries of the scientific ability to measure trace quantities of chemical
compounds in materials, and its illustration of the critical importance of
multidisciplinary research.

Most important, he says, it has given a major new impetus to research that
addresses the closely related questions of "How did life begin on Earth?"
and "Is there life beyond Earth?" A concrete example of this is NASA's
decision to found a new $7 million to $10 million-per-year Astrobiology
Institute specifically for this purpose. Zare is serving as chair of the search
committee for the institute's first director.

MARTIAN METEORITE CONTAINS NO BIOLOGICAL LIFE, RESEARCH TEAM SAYS

The famous Martian meteorite, ALH84001, contains no biological life forms,
according to a Case Western Reserve University researcher and
colleagues.

The team issues this report in the December 4 issue of Nature, duplicating
the methods of a team of scientists from the Johnson Space Center and
Stanford University. In rare counterpoint writings in the "Scientific
Correspondence" section, Nature allowed the Johnson Space Center
team to respond to the group's findings. This paper also appears in the
December 4 issue.

CWRU's Ralph Harvey, senior research associate in the Department of
Geological Sciences, was on the research team. The lead researcher on
the paper was John Bradley from MVA Inc. and the School of Material
Science and Engineering at Georgia Institute of Technology. The third
researcher is Hap McSween from the University of Tennessee.

The trio reports that most of the purported nanofossils or "worm-like
images" are nothing more than lamellae, or fractured surfaces of pyroxene
and carbonate crystals.

Last year, the Johnson-Stanford team announced it found evidence of
nanofossils in the meteorite. Reports of life on Mars spurred the July 4
mission to Mars to look for further evidence of life.

Allan Hills 84001 -- a meteorite the size of a potato -- remains in the
center of a spirited controversy about the possibility of life on Mars. The
meteorite was found in the 1980s in Antarctica by the National Science
Foundation's Antarctic Search for Meteorite Program (ANSMET), headed
by Harvey with headquarters at CWRU.

Harvey, who is currently on his annual expedition to Antarctica to collect
meteorites, commented before leaving November 21 that the Johnson-
Stanford team has always argued that they had used different techniques
to study the meteorite.

Bradley, Harvey, and McSween published a paper last year in Geochimica
et Cosmochimica Acta (GCA), announcing that what the other researchers
observed was formed geologically, not biologically. The Johnson-Stanford
group also announced that these nanofossils were lying on the surface of
the meteorite.

In the first GCA study, which used transmission electron microscope
imagining (TEM), the researchers found non-biological magnetite whiskers
on or near the surfaces of the carbonates. Superficially the whiskers look
like worms, but in fact they have nothing to do with biological processes,
according to Harvey and colleagues.

The latest study took place over the past six months as the researchers
re-examined the meteorite using the new techniques. This time they found
yet another population of worm-like forms that are actually mineral
lamellae formed by non-biological, geological processes. The lamellae
look like worms or nanofossils, but when the specimen is tilted and viewed
from another angle, it clearly shows that the lamellae are attached and
part of the mineral surfaces.

"The surface topography is highly irregular on a nanometre scale, with
emergent lamellae following the major cleavage direction of the substrate,"
Bradley writes in the paper. The researchers have published pictures of
the TEM images to support their findings.

"Peculiar surface structures or segmentation on the worm-like forms are
artifacts from conductive metal coatings applied to the samples for imaging
in the electron microscope. This is not the first time metal coating
artifacts have lead to misidentification of nanofossils in rocks," Bradley
said.

"We have now found two different types of mineral forms in ALH84001
that look just like nanofossils, but they are strictly non-biological origins.
Sometimes even nature has a perverse sense of humor," he added.

Harvey stressed that during this latest study, the team was careful to use
exactly the same methods as the Johnson-Stanford group to lay to rest
any arguments that the research methods had affected the findings.

The worm-like mineral lamellae are commonly found at the fractured
surfaces of planar crystals. Harvey noted that lunar rocks -- in which there
has been no evidence of life found -- contain these same formations.

Does this put an end to the life on Mars debate? "We haven't driven the
final nail in the coffin yet about organisms in this Martian rock, but our
latest article offers a lot of insight that shows these fractures zones in
the rock are incredibly complex," Harvey said, "and that it is very
dangerous to try to draw any hypothesis from a few pictures from here
or there."

National Science Foundation

July 17, 1997

NEW STUDIES OF MARTIAN METEORITE LAUNCHED

The National Science Foundation has awarded grants for seven new projects to
study Martian meteorite ALH84001 in greater depth. The grants are part of a
coordinated program with NASA to further investigate possible traces of
ancient life in the Martian rock.

After the announcement last August that the meteorite may harbor fossils of
ancient Martian life, NSF and NASA called for further research into the
evidence. The agencies set up a coordinated, interdisciplinary program which
included joint review of research proposals. NASA announced on June 19 that
it had awarded 16 individual grants under the program.

NSF's seven new grants, totaling nearly $800,000 for projects over two or
three years, will use advanced instrumentation to further analyze the
provocative rock. Some projects will study ALH84001 itself. Others will
investigate analogous features in terrestrial rocks from environments that
may resemble those of ancient Mars -- hot springs and other extreme habitats
of earthbound microbes -- to provide a better context for understanding the
tiny structures in the Martian rock.

Meteorite ALH84001 is one of about 8,000 meteorites collected in Antarctica
by U.S. researchers. NSF is the lead agency for managing the collection and
distribution of Antarctic meteorites, done in collaboration with NASA and
the Smithsonian Institution. Samples of ALH84001 are being sent to the
researchers from the Antarctic Meteorite Laboratory at NASA's Johnson Space
Center in Houston. The samples, typically only a few grams apiece, are
handled similarly to the lunar samples collected during the Apollo program.

The new research will include scanning the meteorite for extremely
fine-scale alteration of the mineral interface by microbes. Other studies
will focus on the meteorite's carbon isotopes to see if they reflect a ratio
typical of microbial life, and develop a chemical method to fingerprint
biological activity in meteorites using different isotopes of iron, some of
which may be taken up preferentially by living organisms.

Still other projects will look at mineral particles -- oxides and sulfides of
iron -- with potential as "biomarkers" (signs of past life) both in the
Martian meteorite and in bacteria on Earth. Some researchers will attempt
to: fix the temperature and fluid composition under which the meteorite's
minerals formed, presently an area of controversy; develop thermodynamic
models for mineral alteration in hydrothermal environments; and delineate
the rock's temperature history and its past infiltration by fluids.

Institutions receiving the grants are the University of Wisconsin-Madison,
the University of Wisconsin-Milwaukee, California Polytechnic State
University-San Luis Obispo, Iowa State University, Arizona State University,
University of Minnesota, University of California-Santa Cruz, University of
Hawaii, Washington University in St. Louis, and the California Institute of
Technology.

Stanford University

May 29, 1997

Debate over evidence for Martian life in meteorite rages on

Before it was published, Richard Zare suspected that the paper proposing
that a meteorite from Mars once hosted alien life would be a media
sensation. It was.

What Zare didn't expect was the course that the scientific debate has taken.
He thought that the resulting discourse would be skeptical and opinionated,
but also highly reasoned and dispassionate. But because of the high
stakes - nothing less than the first discovery of alien life - and the intensity
of the media spotlight, the scientific interchange has proven to be highly
emotional and highly disruptive, he said.

"Sometimes it is all too easy to forget that the object of this effort is
not to win a debate, but really to understand as much as we can about this
fascinating meteorite," said Zare, the Marguerite Blake Wilbur Professor of
Chemistry.

Since the initial study was published in Science magazine last summer, a
dozen or so scientific papers have been presented at meetings, circulated to
the media and published in scientific journals. A number have attacked
various aspects of the original study, but more have claimed to provide
additional support.

When they released their findings, Zare and his co-authors expected this
sort of give and take. They did not have direct evidence for Martian life,
so they wanted other scientists to examine their work and come to a
collective judgment about whether they were right or wrong. The quality of
much of the criticism and support, however, has not been terribly
impressive, according to Zare and graduate student Simon Clemett, who
took part in the study and has stayed on at Stanford to do additional research
in this area.

"I've become less sanguine about the possibility of a quick answer," Zare
said. "I would have thought by now that our hypothesis would have been
either shot down or accepted. But the situation has proven to be much more
complicated than I first realized."

That said, the two scientists have not seen anything yet that makes them
want to retract their hypothesis. In fact, they argue that the additional
supporting evidence that has been produced slightly outweighs the
criticisms. At the same time, they don't know of any research going on that
is likely to resolve the issue definitively.

The original paper by Zare and his co-authors - NASA scientists David McKay
and Everett Gibson Jr., Kathie Thomas-Keprta of Lockheed Martin, Christopher
Romanek from the University of Georgia and Hojatollah Vali from McGill
University plus Clemett and fellow graduate student Claude R. Maechling with
postdoctoral student Xavier Chillier -- contained four basic lines of
argument to support its pro-life hypothesis: (1) The meteorite, designated
ALH84001, that they examined came from Mars; (2) it contains a unique
pattern of organic compounds that could have been produced by the
fossilization of microorganisms; (3) it contains several unusual mineral
phases commonly produced by microbes; and (4) when examined by an
electron microscope, it reveals textures that appear to be the images of tiny
microfossils. In addition, the features suggestive of biological activity
all appear in the same locations with the rock.

Worm-like shapes

One of the major focal points of criticism has been the nature of the tiny
ovoid and worm-like shapes that the NASA scientists captured with their
high-powered electron microscope and suggested might be microfossils.
From the comments of peer reviewers, the authors knew from the
beginning that these images were probably the weakest link in the
evidence they were presenting. The history of microfossil research is
littered with cases where scientists have been fooled by tiny objects that
look a lot like microorganisms.

One immediate criticism was that these objects were probably just artifacts
of the electron microscopy process. To get the surface features of a rock to
show up in an electron microscope, they must be coated with a thin layer of
gold. If this coating is not uniform, it can obscure the underlying sample's
face and create features that don't exist. Andrew Steele at the University
of Portsmouth has ruled out that possibility by examining an untreated
sample of the meteorite with an atomic force microscope (AFM). The AFM
creates images by scanning the surface with a very fine tip. The fact that
he imaged these features means that they are real, not artifactual.

The critique that Zare considers most serious has been advanced by
William Schopf from UCLA. Schopf, who is a leading authority on the
detection of terrestrial microfossils, has dismissed all the evidence for
Martian life except the fossil-like shapes. If the shapes are not fossils, then
it is possible to explain away the other evidence by various physical
processes. And the only convincing way to determine if these shapes
are fossils, rather than solid splatters of some mineral, is to cut some
open and see if they contain internal structures, he argues.

"The NASA people are trying to do this, but they are finding it very
difficult. The tiny shapes shatter very easily," Clemett said.
Furthermore, Schopf casts doubt on the biological origin of these shapes
by arguing that they are simply too small. The smallest shapes in the
meteorite contain about one-thousandth the volume of the smallest known
living microorganism on Earth. That is not enough space to perform the
basic chemical operations necessary for life, he claims.

Initially Zare and his colleagues did not worry overly about the small size
of these objects because there had been several published reports
claiming that nanobacteria of comparable size had been discovered on
Earth. Clemett has researched the matter since then, only to find a lot of
skepticism about such reports. "People have seen these very small
objects and have claimed to grow them in the lab, but don't seem to know
exactly what they are," he said.

Carbonate globules

Another point of contention has centered around the origin of a series of
unusual carbonate globules that appear to be the centers of the possible
biological activity. NASA scientists argued that these carbonates formed
at relatively low temperature, less than 212 degrees Fahrenheit, more than
3.6 billion years ago while the rock was still on Mars.

One of the strongest attacks on the low temperature origin of the carbonate
minerals was issued by Harry P. McSween Jr. at the University of
Tennessee and Ralph Harvey of Case Western Reserve University. They
argued that the carbonates were formed by a sudden reaction between
rock and boiling, carbon-dioxide-rich water during an impact, probably the
same one that launched the rock from Mars and ultimately caused it to
crash to Earth some 13,000 years ago.

Two other papers, however, have produced results consistent with a
low-temperature origin. John W. Valley and co-workers at the University of
Wisconsin-Madison measured oxygen isotope ratios at a number of
different places within the carbonates and found fluctuations that suggest
a low-temperature formation. Additionally, Joseph L. Kirschvink and co-
workers at the California Institute of Technology found a dramatic
difference in the response between adjacent fragments of the meteorite
when they applied a magnetic field, which Kirschvink said indicates that
it has not been heated above the boiling point of water for at least 4
billion years.

Magnetite criticism

The original team's report of tiny particles of magnetite that are
strikingly similar in shape and size to those created by terrestrial
bacteria that can sense magnetic fields is another source of criticism.
When John P. Bradley of MVA Inc. put a sample of the meteorite under
his transmission electron microscope he observed magnetite in the form
of rods, ribbons and whiskers, many of which contained a screw-shaped
defect that forms at temperatures between 900 to 1400 degrees
Fahrenheit quite different from what the original team found.

"Our problem with Bradley's work is that we don't know where in the
meteorite he is looking," said Clemett. His images appear to be taken of
another part of the meteorite so their relevance to the basic question is
unclear, he added.

"There seems to be a strong element of the blind men and the elephant
at work here. Different researchers are looking at different parts of the
meteorite and coming up with wildly different reports," Zare said.

Another example of this problem is a paper published in the journal Nature
just last week. In it, Edward Scott of Hawaii's Institute of Geophysics and
Planetology announced that his analysis of a sliver of ALH84001
supported a high-temperature origin for the carbonates. However, his
sample did not include the carbonate globules.

Stanford's contribution to the original study was the discovery of
significant amounts of organic material in the meteorite. These
compounds, called polycyclic aromatic hydrocarbons (PAHs), can be
created either by biological or physical processes. But their presence
substantially bolstered the other evidence and played a critical role in
getting the paper through the peer review process.

The Stanford scientists took painstaking efforts to ensure that the PAHs
did not originate from laboratory contamination. But a group of scientists
at Scripps Oceanographic Institute, headed by Jeffrey L. Bada, suggested
that the PAH's were caused by terrestrial contamination during the
13,000 years that ALH84001 sat in Antarctica. According to these
researchers, the same kinds of PAHs turn up in Antarctic ice samples. To
explain the higher concentrations of PAHs measured within the meteorite,
the Scripps scientists conducted an overnight lab experiment that they
said proved that carbonates scavenge PAHs from water and that this can
explain how the PAH levels in the meteorite could build up until they are a
million times higher than those found in the Antarctic environment.

Clemett, together with Chillier and graduate student Seb Gillette, has spent
much of the last nine months looking into the Scripps team's contention.
They discount it entirely, saying that the La Jolla researchers made a
fundamental mistake by not distinguishing between soluble and insoluble
PAHs. Most of the compounds that the Stanford team identified in the
meteorite are highly insoluble. They do not mix well with water, which
makes it extremely difficult for melt water to be the carrier of PAH
contamination. The Stanford team also determined that carbonates do not
scavenge PAHs. When they duplicated the Scripps experiment they found
that most of the PAHs ended up with the carbonate because they were
insoluble, not because the carbonate removed them from the water, as
Bada and co-workers thought.

The Stanford chemists took the matter a step further. They examined
several other Antarctic meteorites and micrometeorites for PAHs. They
found virtually none in some cases. In others, the PAH distributions varied
considerably among samples. If Antarctic melt water were a general
mechanism for PAH contamination, then all the meteorites should be
heavily contaminated, and contaminated in the same way, Clemett argues.

Other than the Scripps team's critique, the news has generally been positive
on the organics front. Colin Pillinger and Ian Wright at the Open University,
working with Monica Grady at the British Natural History Museum in
London, reported detecting an abundance of organic carbon in ALH84001.
They also measured the carbon isotopic ratio of the material and found that
it matched biominerals produced by terrestrial bacteria. Two other papers
also have confirmed the existence of organic material in the meteorite using
different techniques.

Zare confessed that he feels badly about one consequence of the whole
matter: "The need to respond to criticisms has set progress in our lab back
considerably. I never imagined how disruptive this could be." Last August,
he and Clemett had expected to alter their instrument to hunt for amino
acids in the meteorite but have not made much progress.

"Nevertheless, this is a real science story unfolding, warts and all. It
shows that the course of true science, like that of true love, seldom runs
smoothly."